The present invention relates to a heat exchanger for cooling a circulating water of fuel cells and a process for producing the heat exchanger.
A fuel cell system having a high-polymer electrolyte film is known as an automotive fuel cell. In this system, a hydrogen fuel in a stack is turned to proton by the catalytic action of a proton catalyst carried on the high-polymer electrolyte film, and oxygen is supplied to the opposite side of the high-polymer electrolyte film, thereby generating electric potential. It is necessary to cool pure water circulating through the stack by a heat exchanger in order to control the reaction of the fuel cell. This circulating water is brought into a direct contact with the proton catalyst in the system. Thus, it is desired to prevent contamination of the circulating water, for example, caused by ions of metals and the like, in order to protect the proton catalyst. Thus, stainless steel is used for tubes and other parts of the heat exchanger to prevent such contamination.
The inventors have found that the use of stainless steel makes a heat exchanger heavier in weight due to its relatively high specific gravity and makes it larger in size due to its relatively low thermal conductivity, thereby increasing the production cost.
It is an object of the present invention to provide a heat exchanger for cooling a circulating water of a fuel cell, which can assuredly prevent contamination of the circulating water even if a material other than stainless steel is used for the heat exchanger.
It is another object of the present invention to provide a process for producing such heat exchanger.
According to the present invention, there is provided a heat exchanger for cooling a circulating water of a fuel cell. This heat exchanger comprises (1) an aluminum member having an inner surface which defines an inner space in said aluminum member such that said circulating water is allowed to flow through said inner space; and (2) a resin coating layer formed on said inner surface of said aluminum member such that said resin coating layer is in contact with said circulating water when said circulating water flows through said inner space. The aluminum member may comprise a plurality of tubes and a tank connected to the tubes. In the present application, xe2x80x9caluminum alloysxe2x80x9d may be referred to as xe2x80x9caluminumxe2x80x9d for simplification. Thus, aluminum alloys are included in the scope of the term xe2x80x9caluminumxe2x80x9d in the claims. The heat exchanger may comprise a plurality of corrugated fins. The fins and tubes may be alternately arranged and assembled together into a core portion or laminate portion of the heat exchanger.
According to the present invention, it is possible to make a heat exchanger lighter in weight and smaller in size by the use of the aluminum member, thereby decreasing the production cost, as compared with the case of using stainless steel. Furthermore, according to the present invention, a resin coating layer is formed on the inner surface of the aluminum member. With this, it is possible to assuredly prevent contamination of the circulating water which may be caused by ions of metals (e.g., aluminum and metals of flux) and the like.
According to the present invention, there is provided a first process for producing the heat exchanger. The first process comprises (a) providing a core portion of said heat exchanger, said core portion comprising a plurality of tubes, each being made of aluminum, and a plurality of corrugated fins, said tubes and said fins being alternately arranged and assembled together into said core portion; (b) assembling said core portion and a tank made of aluminum into an assembly; (c) brazing said assembly by heating into a brazed assembly; and (d) coating an inner surface of said brazed assembly with a resin coating layer such that said resin coating layer is in contact with said circulating water when said circulating water flows through an inner space of said brazed assembly, said inner space being defined by said inner surface.
According to the present invention, there is provided a second process for producing the heat exchanger. The second process comprises (a) providing a laminate portion of said heat exchanger, said laminate portion comprising a plurality of tubes, each being made of aluminum, and a plurality of corrugated fins, said tubes and said fins being alternately arranged and assembled together into said laminate portion; (b) assembling said laminate portion and a base portion of a tank into a core portion of said heat exchanger, said base portion being made of aluminum; (c) brazing said core portion by heating into a brazed core portion; (d) coating an inner surface of said brazed core portion with a resin coating layer such that said resin coating layer is in contact with said circulating water when said circulating water flows through an inner space of said brazed core portion, said inner space being defined by said inner surface; and (e) mounting a major portion of said tank on said base portion of said tank, thereby forming said tank. This major portion may be made of a resin.